The commercially available magnesium alkoxides are synthesized by the reaction of magnesium metal with alcohols in the presence of reaction initiators like iodine. For example, WO2005/044873 discloses a method for synthesizing spherical magnesium alkoxide particles by reacting magnesium with an alcohol mixture at a temperature below the boiling point of the mixture using I2 as a reaction initiator.
There are several drawbacks associated with the method as provided in the aforesaid PCT application. The spherical magnesium alkoxide particles synthesized by such method are frangible and they do not retain their morphology or particle size during the synthesis of Ziegler Natta procatalyst, especially when the procatalyst synthesis is carried out on a plant scale. Furthermore, a resin produced using the method reported in WO2005/044873 exhibits low resin bulk density which in turn hampers the plant throughput.
A method which attempts to overcome the problems mentioned above has been disclosed in U.S. Pat. No. 5,077,357. It employs dissolution and re-precipitation methodology to incorporate chlorine and the titanium atoms in the matrix of the precursor. In accordance with the method disclosed by U.S. Pat. No. 5,077,357, magnesium alkoxide is dissolved in a halo-hydrocarbon solvent by heating a mixture of magnesium alkoxide, titanium tetra chloride, titanium tetra ethoxide, alcohol, and a phenol derivative at an elevated temperature and the re-precipitation is carried out by the removal of alcohol from the system. The solid semi spherical particles magnesium particles are separated by filtration.
Provided herein below is a brief summary of the known processes wherein iodine has been used as an initiator in the synthesis of the magnesium alkoxide based precursor.
A method for producing the morphology controlled magnesium alkoxide with high mechanical strength and controlled particles size precursor which employs iodine is disclosed in WO2009/130707. It involves the activation of the magnesium metals by iodine to react with a mixture of alcohols at a controlled rate.
A method for synthesis which employs magnesium alkoxide as a carrier material for preparing Ziegler Natta Catalysts with Spherical Morphology has been disclosed in Macromol. React Eng., 2(2008)233-239. It employs Metal halides (MnCl2, FeCl2, CoCl2 and ZnCl2) to synthesize Magnesium ethoxide in the presence of iodine.
Another article, Applied Catalysis A: General 350(2008) 197-206 “Particle growth of magnesium alkoxide as a carrier material for polypropylene polymerization catalyst” provides the details of a process that employs Iodine as a reaction initiator. This article also provides the details of the mechanism by which particles are formed (agglomerates of primary particles) on the surface of magnesium metal. Also, disclosed in this article is the replication of morphology from precursor to catalyst to polymer.
Apart from the abovementioned references, methods for synthesis of the magnesium alkoxide precursor using halogen initiators and activators are taught in US 2009/0112027, US2009/0233793, US2009/0148702, U.S. Pat. No. 5,077,357 and WO/2009/130707.
The drawback of the precursor prepared through the iodine activator is that its particle strength is low and therefore it is prone to breakage. This results in the formation of fines during catalyst synthesis. As a result a polymer obtained through the catalyst also contains very high level of fines which causes frequent choking problems in a commercial plant. Furthermore, the precursor prepared through iodine activator form iodine compounds which remain with the precursor. This adversely affects the performance of the catalyst.
In view of the above, there is therefore exists a need for a method to synthesize a magnesium alkoxide based precursor with high particle strength that overcomes the drawbacks associated with the prior art.